1. Field of the Invention
The invention is directed to an analog telephone subscriber terminal apparatus which is remotely connected to an exchange by a subscriber terminal line and which comprises means for evaluating, storing and displaying data that is received from the exchange while simultaneously outside of the "idle" switching state and in the "on-hook" state, the data being connected with additional functions.
2. Description of the Prior Art
Typically, a telephone subscriber terminal apparatus must be high-ohmic in the on-hook state since, in the idle switching state, the supply current in the associated terminal circuit is provided at a high resistance to save current. Another reason for the high-ohmic requirement is that, in the indication circuit for the evaluation of subscriber line signaling, a low event threshold is switched effective. Further, it must also be taken into account that several telephone subscriber terminal apparatuses may be connected in parallel.
For these reasons, an additional local current supply, fed from the current network, is normally used to supply the means for providing additional functions to the telephone subscriber terminal apparatus. Such additional functions include, for example, displaying the name and phone number of the calling subscriber.
An object of the present invention, therefore, is to provide an analog telephone subscriber terminal apparatus which does without such a local current supply, derived from the current conducting network, in order to realize the desired additional functions. This object is achieved in an a analog telephone subscriber terminal apparatus having a current supply device which draws current from a subscriber line and then provides the supply current, when switched effective, for the means for realizing the additional functions--the device limiting the increased subscriber line loop current such that it does not provide a loop closure.
In an embodiment of the present invention, the means for realizing additional functions is remotely connected to the exchange by the subscriber terminal line, as is the remote telephone subscriber terminal apparatus in connection with the "telephone" function. For such purpose, a current supply device, which receives current from the subscriber terminal line, is provided as a component of the telephone terminal apparatus. However, this current supply device is activated only for the duration of the transmission of the data concerning such additional items of information. This is the case only when the apparatus is outside of the idle switching state and, thus, during a time when the event threshold in the indication circuit at the side of the exchange is "high" for the subscriber line signal relative to the idle operating state. In this stage, it is also possible both to make a sufficient supply current available for the current supply device, and to limit the current to such an extent that its use is not falsely interpreted as the closure of the subscriber line loop.
In an embodiment, the current supply device is supplemented by a high-ohm chargeable energy storage element that provides the initial required supply current for a data transmission recognition circuit. The current supply device is thereby realized in the form of a current regulator circuit which can be activated and deactivated by the recognition circuit. The regulator circuit, therefore, takes over the current supply for the data transmission recognition circuit. In this embodiment, it is ensured that a supply current is available for the data transmission recognition circuit at the beginning of a data transmission, without violating the requirement that the telephone subscriber terminal apparatus have a high resistance at the time before the data transmission. During the course of the data transmission, it is also ensured that a sufficient supply current is available for the evaluation means while the relatively low-resistance state of the telephone subscriber terminal apparatus which arises does not last longer than the duration of the data transmission.
In an embodiment, a filter circuit and a rectifier circuit are also provided which, at the beginning of a telephone call, provide the charge current for the energy storage element at low resistance from the AC call current. This embodiment is important for the realization of additional functions which are not to be executed until after the arrival of the first call and which represent a rapid charge device for the energy storage element. As a result, disturbing delays in the activation of the current supply device, due to the charge time required for the charging of the energy storage element, cannot occur when the telephone subscriber terminal apparatus is used in quick succession.
Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments and from the drawings.